1. Field of the Invention
The present invention relates to a semiconductor integrated circuit including a spiral inductor which is formed of a spiral-line-shaped electrically conductive layer, with dummy wiring lines being disposed on peripheral areas of the spiral inductor, and more particularly to a semiconductor integrated circuit for a radio-frequency receiving element.
2. Description of the Related Art
In the modern fabrication generation, such a design rule has begun to be proposed that when a spiral inductor is to be formed of a metal wiring layer in a semiconductor integrated circuit for a radio-frequency receiving element, for instance, dummy wiring lines which are formed of metal wiring layers are disposed to have a predetermined coverage on peripheral areas of the spiral inductor. With the adoption of this design rule, non-uniformity in chemical mechanical polishing (CMP) and peeling of wiring lines can be prevented. For example, according to one proposed design rule, in a case where patterns of wiring layers are present on a region with a predetermined area, which includes a spiral inductor and peripheral areas of the spiral inductor but the coverage of these patterns of the wiring layers does not reach a prescribed level, patterns of dummy wiring lines are automatically and randomly generated. The coverage of the wiring layers, in this context, means the ratio of wiring patterns, that is, the area occupied by wiring patterns within a predetermined region in each of multiple wiring layers.
It has been clarified that in the case where dummy wiring patterns are automatically disposed near the spiral inductor, when a dummy wiring pattern is generated under the spiral inductor, a parasitic capacitance and a parasitic inductance will occur and the inductor-quality factor Q of the spiral inductor deteriorates. Thus, there is a demand for the establishment of a proper design rule relating to the arrangement of the dummy wiring lines. The resistance value of the spiral inductor is expressed by R, the inductance value of the spiral inductor is expressed by L and the angular frequency of a radio-frequency signal which is applied to the spiral inductor is expressed by ω, the following relationship is established: Q=ωL/R.
When the patterns of the dummy wiring lines are to be disposed and the patterns are not automatically generated but are manually disposed, eddy current may occur in the dummy wiring lines, depending on the shapes of the patterns. Thus, the Q of the spiral inductor may also be degraded in the case of manually disposing the dummy wiring lines.
Jpn. Pat. Appln. KOKAI Publication No. 2002-110908 discloses that a spiral inductor, which is formed of a spiral-line-shaped electrically conductive layer, is formed on a substrate, and a trench for device isolation is formed in the substrate surface such that a projection portion, which becomes a dummy device region with an upper surface for controlling a CMP step, is formed on a region excluding a region immediately under the spiral-line-shaped electrically conductive layer.